1. Field of the Invention
This invention relates to a magnetic disk cartridge rotatably housing a very thin disk-shaped magnetic recording medium, i.e. a magnetic disk sheet.
2. Description of the Prior Art
Magnetic disk sheets, i.e. floppy disks, are widely used as recording media for computers because they are easy to handle and low in cost. The magnetic disk sheet comprises a disk-like base sheet made of flexible polyester or the like, and magnetic material layers overlaid on opposite surfaces of the disk-like base sheet. The magnetic disk sheet is rotated for magnetically recording information on the magnetic material layers by use of a magnetic head.
In general, writing of the information on the magnetic disk sheet or reading of the information therefrom is carried out by rotating the magnetic disk sheet and, at the same time, sliding the magnetic writing head or the magnetic reading head over the magnetic recording surface in the radial direction of the magnetic disk sheet. Therefore, when conformity of the surface of the magnetic disk sheet with the magnetic head is low or dust or the like enters the gap of the magnetic head in the course of writing or reading of the information, the signal input and/or signal output fluctuates, or drop-outs occur.
Particularly, in the case of a 3.5-inch type small magnetic disk cartridge, the outer case is formed of a hard material, and a dust-preventing shutter is disposed at an opening into which the magnetic head is to be inserted, thereby to improve reliability. Also, a disk-like liner formed of a rayon nonwoven fabric, a polyester nonwoven fabric or the like is disposed between the magnetic disk sheet and an inner wall surface of the case so that the liner slightly contacts the recording surface of the magnetic disk sheet. When the magnetic disk sheet is rotated, the liner removes dust or the like from the surface of the magnetic disk sheet.
As mentioned above, the liner formed of rayon, polyester or the like has heretofore been shaped in a disk-like form. The liner is made by cutting a sheet-like material by use of a punch having a complicated shape. However, with the punching out method, it is not always possible to maintain good cutting characteristics (sharpness), and the fibers of the liner remain in a form of ravelings at the cut section and protrude out of the case.
Accordingly, it has been proposed to make a polygonal liner by using a linear cutter such as a scissors which can maintain good cutting characteristics for long periods, and forming the outer shape of the liner into a polygonal shape such as an octagon.
However, the internal peripheral wall of the case for general disk-shaped liners is shaped in a circular shape conforming with the outer shape of the liner. Therefore, the polygonal liner cannot always be loaded into the case because of interference of the corners of the polygonal liner with the circular peripheral wall of the case. Also, when the size of the polygonal liner is decreased to such an extent that the polygonal liner can be loaded into the case, the outer shape of the polygonal liner becomes smaller than the recording surface of the magnetic disk sheet, and the cleaning effects of the polygonal liner becomes insufficient. On the other hand, the case may be fabricated to have linear internal peripheral walls in conformity with the outer shape of the polygonal liner. However, in this case, the disk-shaped liner cannot be loaded into said case. Thus the conventional techniques are not efficient and lack flexibility in application.